1. Field of the Invention
The present invention relates to a method for manufacturing polycrystalline silicon thin film transistors with a laser-recrystallized active layer. More particularly, the present invention forms a large silicon grain structure of the active layer without an additional mask.
2. Description of the Prior Art
In growing the thin film transistor display from a low temperature polycrystalline silicon thin film transistor (LTPS-TFT) extending over an amorphous silicon thin film transistor (a-si TFT), it has been proposed to use various conventional display devices, such as, personal digital assistant, digital camera, cell phone so as to substantially enhance resolution, brightness, size and electromagnetic disturbance by LTPS-TFT display.
However, such conventional laser annealing LTPS-TFTs process has proven to be unsatisfactory. When forming the active layer of transistor after the laser recrystallization is used to fabricate LTPS-TFTs, the resulting silicon grain structure typically lacks uniform structure. Such nonuniformity is due to the small and irregular silicon grain which causes the difference of electric characteristic between elements. But, when the laser recrystallization are formed after the active layer of transistor are used to fabricate LTPS-TFTs, the resulting surface tension causes shrinkages, which are caused by melting the silicon film. Therefore, the conventional method can not be used to produce LTPS-TFTs.
The structure of a TFT and silicon-on-insulator metal oxide semiconductor field effect transistor (SOI-MOSFET) is an insulated layer with poor thermo conductivity under the active layer. When a working current of the device is large a high temperature in the active layer can suddenly be produced, such that a mobility rate of a carrier of the active layer is diminished, so that the relative study reports the division of channel W into parallel connection of many small channels W1 to overcome self-heating effect as shown in FIG. 7. It shows a conventional view of settlement of self-heating effect. More particularly, the conventional division of channel W into two parallel connection of many small channels W1 cannot be sufficiently overcome by dispersing heat during the large working current, unlike the present invention.